[Bug-tar] Possible tar bug with -C, --from-files stdin and --null

[Daryl Tester]

(Oops, sent from wrong address - moderator, please ignore previous post).

Hi.

I seem to have hit a possible bug with gnu-tar (versions 1.19 and 1.16)
trying to use the --null form of --from-files (-T) in conjunction with
-C (change directory).  Apologies for not trying it on the latest tar -
I don't have a non-production system to compile that version on at the
moment.

The background is that I'm doing "programmatic backups", where I'm
selecting a set of files to be backed up under script control, then
feeding it into tar via stdin.

I'll show by examples - it's quite possible the misunderstanding is
mine.


Using -C and -T (stdin) works (without --null):

$ echo 'hosts' | tar -cf - -C /etc -T - | tar -tvf -
-rw-r--r-- root/root       221 2008-06-06 11:53 hosts

Confirming null terminated string is correct:

# echo -ne 'hosts\0' | hexdump -C
00000000  68 6f 73 74 73 00                                 |hosts.|
00000006

Using -T (stdin) and --null works:

$ echo -ne '/etc/hosts\0' | tar -cf - --null -T - | tar -tvf -
tar: Removing leading `/' from member names
-rw-r--r-- root/root       221 2008-06-06 11:53 etc/hosts

Using -T, -C and --null "fails" to archive the specified file, in that
it seems to default to a behaviour as if I has specified ".".

$ echo -ne 'hosts\0' | tar -cf - -C /etc --null -T - | tar -tvf - | head
tar: Removing leading `/' from member names
drwxr-xr-x root/root         0 2008-09-22 20:22 etc/
drwxr-xr-x root/root         0 2008-03-27 04:00 etc/gnupg/
drwxr-xr-x root/root         0 2008-04-08 07:14 etc/opt/
drwxr-xr-x root/root         0 2008-04-08 07:14 etc/news/
-rw------- root/root         1 2008-03-26 00:38 etc/at.deny
lrwxrwxrwx root/root         0 2008-06-06 11:53 etc/grub.conf -> 
../boot/grub/grub.conf
-rw-r--r-- root/root     10814 2006-02-21 08:25 etc/ltrace.conf
-rw-r--r-- root/root       112 2008-02-22 09:06 etc/mail.rc
-rw-r--r-- root/root        59 2006-01-31 23:36 etc/filesystems
lrwxrwxrwx root/root         0 2008-06-06 13:45 etc/rc -> rc.d/rc


Also, the "-C" option appears to be sensitive to where it's placed on
the command line - I had tar report that it couldn't archive the
specified file due to it not being found which was resolved by
placing -C before the --files-from option, but the documentation
didn't give (to me) any sense that this would be an issue:

$ echo 'hosts' | tar -cf - --files-from - -C /etc | tar -tvf - 
tar: hosts: Cannot stat: No such file or directory
tar: Error exit delayed from previous errors
$ echo 'hosts' | tar -cf - -C /etc --files-from - | tar -tvf - 
-rw-r--r-- root/root       255 2007-12-26 18:24 hosts


I've subscribed to the list, so if there are any further requests
for clarifications or what-not feel free to either fling them my
way or back onto the list.  Thanks.


-- 
Regards,
  Daryl Tester

"A long time ago, I stopped thinking that 'User must click OK to
 scary-looking message' was any sort of road bump for malware."
  -- Valdis Kletnieks